Various electronic systems are presently known for detecting defects in continuous lengths of material. For example, U.S. Pat. No. 3,584,225 relates to a yarn inspection device which uses optical devices and electronic circuitry to detect defects in yarn. U.S. Pat. No. 3,114,797 relates to a television system for detecting differences or changes in shape, size, color, intensity or texture. Such differences or changes are detected by comparing a scene at one instant with an image produced from the same scene after a time delay. U.S. Pat. No. 3,700,903 relates to detection systems wherein a coherent light beam is used to scan the surface of an object in a repetitive pattern. An output signal is produced by light reflected from the object for determining characteristics of the surface of the object.
My U.S. Pat. Nos. 4,232,336 and 4,240,110, incorporated herein by reference, relate to the inspection of elongated material for surface irregularities for determining certain characteristics such as count.